Maybe a story about Morty's growth and how he changes over time. He starts off as a somewhat naive boy but gradually becomes more confident and capable through his experiences with Rick, like learning to handle difficult situations on their inter - dimensional travels.
A popular story might be Morty's experience with an alien invasion in his own dimension. He has to use the skills he learned from Rick to try and save his family and the world.
By putting them in situations where they have to rely on each other. For example, if they are trapped in a dangerous dimension. This would force them to interact and potentially grow closer.
You can start by looking at popular fanfiction websites like Archive of Our Own. They have a tagging system, so you can search for 'Rick and Morty' and then look for tags related to Morty specifically. Another option is to join Rick and Morty fan groups on social media platforms and ask for recommendations from other fans.
Morty's character often develops more confidence. When he time travels, he's forced to make decisions on his own without Rick always there to guide him. For example, if he's in a past where Rick is unavailable, he has to figure out how to deal with the situation. This makes him grow bolder.
Well, an 'Evil Morty' fanfic in the 'Rick and Morty' universe can be really interesting. Evil Morty is such a complex character. In these fanfics, he could be explored further in terms of his motives. Maybe he's tired of being in Rick's shadow or he has some grand plan to take over the multiverse that wasn't fully shown in the show. Fanfics give the writers the freedom to expand on his backstory and what makes him tick.